i recommend mock-1.1.7 for building. unfortunately at rh it's not
required to be able to build src.rpm is mock, they use only rpmbuild (!)
which of course cause a few dozen of packages won't build:-(
imho it'd be useful something like this for rhel too:
http://fedoraproject.org/wiki/FTBFS

I don't know where you get your info but everything is built in mock.
-sv